Fix cmake configure on windows

Author: toroidal-code

.github/workflows/test.yml

@@ -30,21 +30,15 @@ jobs:
       run: |
         echo "CC=clang-18" >> $GITHUB_ENV
         echo "CXX=clang++-18" >> $GITHUB_ENV
-      if: ${{ matrix.os == 'ubuntu-latest' && matrix.compiler != 'native'}}
+      if: ${{ matrix.os == 'ubuntu-latest' && matrix.compiler != 'native' }}
 
-    - name: Use LLVM and Clang for Windows
-      run: |
-        echo "CC=clang" >> $GITHUB_ENV
-        echo "CXX=clang++" >> $GITHUB_ENV
-      if: ${{ matrix.os == 'windows-latest' && matrix.compiler != 'native'}}
+    - name: Configure with Clang for Windows
+      run: cmake -B build -DCPPSPEC_BUILD_TESTS=YES -DCMAKE_C_COMPILER="clang" -DCMAKE_CXX_COMPILER="clang++"
+      if: ${{ matrix.os == 'windows-latest' && matrix.compiler == 'llvm' }}
 
     - name: Configure with default compiler
       run: cmake -B build -DCPPSPEC_BUILD_TESTS=YES
-      if: ${{ matrix.compiler == 'native'}}
-
-    - name: Configure with specific compiler
-      run: cmake -B build -DCPPSPEC_BUILD_TESTS=YES -DCMAKE_C_COMPILER="$CC" -DCMAKE_CXX_COMPILER="$CXX"
-      if: ${{ matrix.compiler != 'native'}}
+      if: ${{ matrix.compiler == 'native' || matrix.os != 'windows-latest' }}
 
     - name: Build
       run: cmake --build build --config Release